Systems and methods for remotely monitoring the exhaust gas composition of motor vehicles are known. Examples of such systems and methods are described in, for example, U.S. Pat. Nos. 5,210,702, 5,319,199, 5,401,967, 5,591,975, 5,726,450, 5,797,682, and 5,831,267, each of which is hereby incorporated herein by reference in its entirety. Commercial systems such as the AccuScan™ Remote Sensing Device (RSD) 3000 and the AccuScan™ Remote Sensing Device (RSD) 4000 offered by Environmental Systems Products, Inc. are also known.
Despite steady advances in the sophistication and robustness of remote emissions sensing (RES) systems, many RES systems remain susceptible to erroneous readings or inconsistent results. Unfortunately, such drawbacks can sometimes lead to relatively high incidences of discarded data or relatively high incidences of “flagged” test results, which indicate suspect results. These and other problems can reduce the benefits of an RES system.